1. Field of the Invention
The present invention relates to a coloring resin composition. More specifically, the present invention relates to a coloring resin composition for use in coloring molded articles of thermoplastic resin, and a colored resin molded article obtained by using the coloring resin composition.
2. Description of the Related Art
Conventional coloring resin compositions for use in coloring molded articles of thermoplastic resin or manufacturing colored resin molded articles, include powdered dry color in which pigment and a dispersing agent are mixed; liquid color or paste color in which pigment is dispersed in a dispersing agent that is in liquid state at room temperature; and pellet-, flake- or bead-shape coloring pellets (also termed coloring compound) or master batches in which pigment is dispersed in resin that is in solid state at room temperature. The master batches are the same as the coloring pellets in that pigment is dispersed in resin that is solid at room temperature. However, the coloring pellets are different from the master batch in that the coloring pellets are molded as they are while the master batches are diluted first with appropriate thermoplastic resin (resin for dilution or resin to be colored) before being molded, since the pigment concentration is high.
The coloring resin compositions are selected for application on the basis of their characteristics. Among them, master batches are preferably used due to ease of handling and in consideration of the working environment during the application. Master batches are high in pigment concentration and have little effect on various properties such as heat resistance and strength of thermoplastic resin to be colored. Additionally, pigment dispersibility is required to be higher than previously, as polyolefin resin has been molded with improved precision and accelerated speed.
Generally, the following dispersing agents are used in order to add pigment dispersibility in a master batch. The agents include stearic acid; metallic soap such as zinc stearate, magnesium stearate, aluminum stearate and calcium stearate; ethylene bisamide; hydrocarbon wax such as polyethylene wax and polypropylene wax; and derivatives thereof such as wax consisting of an acid modified product or a hydroxyl group modified product.
However, when high pigment dispersibility is required in order to mold articles by high-speed spinning at a diameter of 10 and several microns, or by forming into films, the above-noted dispersing agents have not provided sufficient dispersibility.
In Japanese Unexamined Patent Application Publication No. 7-53772, a compound expressed by the following chemical formula is used as a dispersing agent of a coloring resin composition:
(CH3xe2x80x94(CH2)xxe2x80x94CH2xe2x80x94O(CH2CH2O)nH 
wherein x is 28 to 48 on average, and n is 1 to 16.
This dispersing agent provides more preferable results than does a conventional agent. However, such problems due to lack of pigment dispersion are still found as thread breakage during spinning, clogging filters of melt spinning apparatus, and the development of lumps on a film surface. Moreover, although the composition may be spun at high speed or formed into a film, a molded article thereof is not often practically strong enough when higher mechanical physical strength is required for the molded article.
In order to solve the above-noted problems and enhance pigment dispersibility, attempts to improve the processing methods of master batches, to use a high-powered kneading machine, and so forth have been made. However, sufficient pigment dispersibility has not yet been achieved therefrom.
Accordingly, it is an object of the present invention to provide a coloring resin composition having excellent pigment dispersibility and high coloring properties. The coloring resin composition can be used as a master batch without giving physical inhibitions of 5% or higher to each mechanical strength of resin to be colored, such as tensile strength, flexural modulus and impact strength. It is another object of the present invention to provide a colored resin molded article by using the coloring resin composition.
In order to achieve the above-noted objects, a coloring resin composition according to a first aspect of the invention includes a dispersing agent, a pigment and a thermoplastic resin. The following Formula 1 expresses the dispersing agent, and the thermoplastic resin is a metallocene polyolefin:
CnH2n+1(OCH2CH2)mOH xe2x80x83xe2x80x83Formula 1 
wherein n is an integer of 1 to 100, and m is an integer of 1 to 100.
A coloring resin composition according to a second aspect of the invention is provided by removing water from a mixture of a dispersing agent expressed by the same Formula 1 as above, a pigment, water and a metallocene polyolefin.
Subsequently, the coloring resin composition of the present invention is used to provide a colored resin molded article according to the present invention. The coloring resin composition of the present invention has excellent pigment dispersibility and good coloring properties, so that colored resin molded products having excellent mechanical strength and high coloring properties can be manufactured therefrom.
The coloring resin composition according to the present invention can be used as a master batch or coloring pellets not only for colored resin molded articles but also for others such as ink, coating paint and adhesive.
The embodiments of the present invention will be explained in detail below.
The metallocene polyolefin is a general term of polyolefin in which metallocene is used as a catalyst for polymerization. This polymer is a high molecular weight polymer having higher monodispersibility and a narrower molecular weight distribution (for instance, Mw/Mn less than 2 in case of metallocene polyethylene) than a polymer in which conventional Ziegler catalyst, Ziegler-Natta catalyst or the like is used. The polymer obtained thereby has low crystallinity and is nearly amorphous. The density and melting point thereof are significantly lower than those of general polyolefin consisting of the same monomer that is polymerized by a non-metallocene catalyst.
Such polymer and the dispersing agent of the above-noted Formula 1 are used for the coloring resin composition, so that a large amount of pigment can be dispersed quite evenly. Accordingly, the composition can provide molded articles having excellent mechanical strength without such problems as breakage of films due to lack of pigment dispersibility, and is also suitable for spinning and forming into films. Moreover, since pigment dispersibility is preferable, the coloring resin composition also has excellent coloring properties.
According to the knowledge of the present inventors, the water with which the pigment particles are wetted evaporates during a melting and kneading process when a mixture of a dispersing agent, pigment and resin contains water, and the surface of the pigment particles which are refined by shearing during kneading is coated with molten thermoplastic resin, thus preventing the re-agglomeration of pigment particles and providing a resin composition having excellent pigment dispersibility. The present inventors also found that the dispersibility of pigment improves by carrying out the flushing of pigment from the aqueous phase to a resin phase slowly at the temperatures near the boiling point of water. The use of metallocene polyolefin having a lower melting point than general polyolefin has also the advantage of carrying out such flushing easily and effectively.
The dispersing agent used in the coloring resin composition of the present invention containing a dispersing agent, a pigment and a thermoplastic resin is expressed in the following Formula 1:
CnH2n+1(OCH2CH2)mOH xe2x80x83xe2x80x83Formula 1 
wherein n is an integer of 1 to 100, and m is an integer of 1 to 100.
When n exceeds 100 in the formula above, pigment dispersibility may decline. At the same time, the melting point of the dispersing agent rises, so that processability may deteriorate when resin to be colored has a low melting point. Moreover, when m exceeds 100, the dispersing agent may start decomposing and foaming due to heat during the processing of the coloring resin composition. It is preferable that n ranges from 26 to 50 and m ranges from 4 to 100. Furthermore, it is preferable to use a dispersing agent having a melting point of 60xc2x0 C. to 120xc2x0 C. in consideration of the flushing temperature mentioned above. This is because pigment may not be well dispersed when a dispersing agent is not melted at the flushing temperature. Moreover, the melting point of a dispersing agent is preferably 60xc2x0 C. or higher in consideration of smooth material transportation during extrusion processing. It is also preferable that the melting point is 120xc2x0 C. or lower in consideration of quick dispersibility into resin to be colored. The melting point in the present invention is the peak temperature of a melting point measured under a nitrogen gas stream and the temperature increase rate of 10xc2x0 C./minute by a differential scanning calorimeter.
A base thermoplastic resin includes metallocene polyolefin that is polymerized by the catalyst of a metallocene compound. Metallocene polyolefins are highly compatible with other resins (polyolefins). Specifically, a master batch of general polyethylene is not compatible with, for instance, polypropylene (resin to be colored), while metallocene polyethylene is compatible with polypropylene. Thus, the coloring resin composition of the present invention is generally and widely applicable as a master batch. Additionally, molded articles having excellent mechanical properties can be provided by evenly mixing the composition with resin to be colored. The reason for high compatibility is thought to be that metallocene polyolefins have low crystallinity and only a few crystals are formed evenly and finely, so that the crystal growth of resin to be colored is not prevented. Additionally, this polymer contains many tie molecules, and has the advantage of providing molded articles having excellent mechanical strength (impact strength, tensile strength and so forth).
The metallocene compound is a general term of compounds in which ligands including at least the one having a cyclopentadienyl skeleton coordinate to a tetravalent transition metal such as titanium, zirconium, nickel palladium, hafnium, niobium and platinum.
Examples of the ligands having a cyclopentadienyl skeleton include cyclopentadienyl group; alkyl-substituted cyclopentadienyl groups such as methylcyclopentadienyl group, ethylcyclopentadienyl group, n- or i-propylcyclopentadienyl group, n-, i-, sec-, or tert-butylcyclopentadienyl group, hexylcyclopentadienyl group and octylcyclopentadienyl group; alkyl disubstituted cyclopentadienyl groups such as dimethylcyclopentadienyl group, methylethylcyclopentadienyl group, methylpropylcyclopentadienyl group, methylbutylcyclopentadienyl group, methylhexylcyclopentadienyl group, ethylbutylcyclopentadienyl group and ethylhexylcyclopentadienyl group; alkyl polysubstituted cyclopentadienyl groups such as trimethylcyclopentadienyl group, tetramethylcyclopentadienyl group, and pentamethylcyclopentadienyl group; cycloalkyl substituted cyclopentadienyl groups such as methylcyclohexylcyclopentadienyl group; indenyl group; 4, 5, 6, 7-tetrahydroindenyl group; fluorenyl group; and so forth.
Examples of ligands, besides the ones having a cyclopentadienyl skeleton, include monovalent anion ligands such as base and bromine; bivalent anion chelate ligands; hydrocarbon groups; alkoxides; amides; arylamides; aryloxides; phosphide; arylphosphide; silyl groups; substituted silyl groups; and so forth. Examples of the hydrocarbon groups include the ones having about 1 to 12 carbon atoms. For example, the hydrocarbon groups include alkyl groups such as methyl group, ethyl group, propyl group, butyl group, isobutyl group, amyl group, isoamyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, cetyl group, and 2-ethylhexyl group; cycloalkyl groups such as cyclohexyl group and cyclopentyl group; aryl groups such as phenyl group and tolyl group; aralkyl groups such as benzyl group and neophyl group; nonylphenyl group; and so forth.
Specifically, examples of the metallocene compounds in which ligands including the one having a cyclopentadienyl skeleton form coordinate bonds, include cyclopentadienyltitanium tris(dimethylamide); methylcyclopentadienyltitanium tris(dimethylamide); bis(cyclopentadienyl)titanium dichloride; dimethylsilyltetramethylcyclopentadienyl-tert-butylamidozirconium dichloride; dimethylsilyltetramethylcyclopentadienyl-p-n-butylphenylamido zirconium dichloride; methylphenylsilyltetramethylcyclopentadienyl-tert-butylamidohafnium dichloride; dimethylsilyltetramethylcyclopentadienyl-tert-butylamidohafnium dichloride; indenyltitanium tris(dimethylamide); indenyltitanium tris(diethylamide); indenyltitanium bis(di-n-butylamide); indenyltitanium bis(di-n-propylamide); and so forth.
Such metallocene compounds can be used as a catalyst system to which methylaluminoxan, boron compounds, or the like is added as cocatalyst. In this case, it is preferable that the cocatalyst 1 to one million molar times the metallocene compound is added thereto.
Examples of polyolefins include polyethylene, polypropylene, copolymer (random or block copolymer) of ethylene and propylene, and copolymer of ethylene or propylene and xcex1-olefins (excluding ethylene or propylene) and so forth. Or low grade polymers by the thermal decomposition of the polyolefins mentioned above may be applicable. They can be used singly or in combinations.
Examples of the xcex1-olefins include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 4-methyl-1-pentene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and the like. As the xcex1-olefin that is copolymerized with ethylene, it is preferable to use 1-butene, 1-hexene and 1-octene. As the a-olefin that is copolymerized with propylene, it is preferable to use 1-butene and 1-hexene.
Preferably, use can be made of metallocene polyethylene because of its low melting point and low density.
The melting point of polymer ranges preferably from 40xc2x0 C. to 120xc2x0 C., more preferably from 50xc2x0 C. to 100xc2x0 C. Particularly, when the melting point of polymer is 100xc2x0 C. or lower, the processing temperature can be set at around 90xc2x0 C., thus maximizing flushing efficiency, which is preferable. When the melting point is too low, the polymer may become sticky at room temperature, resulting in poor operation. Additionally, the drying step of the coloring resin composition may become troublesome. The density of the polymer is preferably 0.19 g/cm3 or smaller in consideration of the relationship with the melting point mentioned above, more preferably 0.87 g/cm3 or greater in consideration of handling, and further preferably 0.875 to 0.905 g/cm3.
In a preferable embodiment, a polymer with the melt flow rate (MFR) of 0.1 to 400, and more preferably 5 to 250 can be chosen. When MFR is smaller than 0.1, the compatibility of the polymer with resin to be colored may decline, causing unevenness of color on molded articles and providing negative effects on various properties. On the other hand, when MFR is beyond 400, it may become difficult to manufacture the coloring resin composition and various properties such as the strength of molded articles may deteriorate. Here, the MFR is measured according to JIS K7210.
The pigment may be at least one type selected from conventional organic pigments and inorganic pigments which have been conventionally used for coloring printing inks, paints or thermoplastic resins, and there is no particular limitation.
Examples of the organic pigments include azo pigments such as azo lake, Hansas, benzimidazolones, diarylides, pyrazolones, yellows and reds; polycyclic pigments such as phthalocyamines, quinacridones, perylenes, perinones, dioxazines, anthraquinones and isoindolins; and Aniline Black. Examples of the inorganic pigments include inorganic pigments such as titanium oxide, titanium yellow, iron oxide, ultramarine blue, cobalt blue, chromic oxide green, Lead Yellow, cadmium yellow and cadmium red; and carbon black pigments. They can be used singly or in combination.
These pigments may be in any form of a dry powder, wet cake containing water before submitted to a drying process, or a mixture thereof.
The coloring resin composition according to the present invention contains at least dispersing agent, pigment and metallocene polyolefin mentioned above. The composition can be used as a master batch that contains pigment at high concentration and is diluted with resin to be colored during a molding process. Or the composition can be used as coloring pellets that have relatively low pigment concentration and are molded as they are without being diluted with resin to be colored. Mixing ratios of each component in the composition are not particularly limited, and may be appropriately selected in accordance with its uses, applications and so forth.
For instance, when the coloring resin composition is used as coloring pellets, it is preferable that the pigment is contained at 0.01 wt. % or more in consideration of tinting strength, the hue and so forth. Moreover, in consideration of the appearance of molded articles (for example, no lumps due to pigment coagglomeration), the content thereof is preferably 40 wt. % or less. When the coloring resin composition is used as a master batch, the pigment is preferably contained at 0.01 wt. % or more in order to economically provide the targeting hue and tinting strength, and in consideration of pigment dispersibility and so forth the content thereof is preferably 90 wt. % or less, and more preferably 20 to 80 wt. %.
A dispersing agent and thermoplastic resin are preferably mixed at the ratio of 0.01 to 30 wt. % and 10 to 99.9 wt. %, respectively.
The coloring resin composition may also contain various additives such as wax, antioxidant, ultraviolet light absorber and a surface active agent within a range that does not inhibit the effects of the present invention, if necessary.
Subsequently, a coloring resin composition according to another present invention is provided by removing water from the mixture of the dispersing agent, pigment, water and metallocene polyolefin described above. The same characteristics as those of the composition mentioned above are omitted herein, and other characteristics are explained below.
The water may be tap water, distilled water, ion-exchanged water, hard water, soft water or the like, and is used with no particular limitation. However, it is preferable that the water contains no components (coarse particles, dissolved matters, ions, and so forth) that may limit uses or applications of the coloring resin composition.
It is preferable that the mixture containing the dispersing agent, pigment, water and metallocene polyolefin is prepared by adding pigment to the aqueous solution of a dispersing agent or the aqueous dispersion of a dispersing agent so as to provide further preferable pigment dispersion. Pigment dispersibility improves by using the aqueous medium of a dispersing agent instead of directly mixing the dispersing agent. The aqueous medium here refers to the mixture of a dispersing agent and water, the aqueous solution of a dispersing agent when the dispersing agent is soluble in water or the aqueous dispersion of a dispersing agent when the dispersing agent is not soluble in water, or the combination thereof. Accordingly, the mixture becomes suitable for spinning, film forming, and so forth that require high dispersibility of pigment. Moreover, the mechanical properties of molded articles become further preferable. In this case, it is preferable that the mixture contains 1 to 30 weight parts of the aqueous medium of a dispersing agent, 0.01 to 90 weight parts of pigment, and 1 to 90 weight parts of thermoplastic resin.
The concentration of a dispersing agent relative to water (or concentration of a dispersing agent in an aqueous medium) is preferably 1 wt. % or more in order to efficiently provide pigment dispersibility and 80 wt. % or less in consideration of handling and practicality. The concentration of 5 to 50 wt. % is particularly preferable. When powdered dry pigment is used, the concentration of water is preferably 5 wt. % or more in order to fully provide the effects of adding water and preferably 200 wt. % or less in consideration of efficiency during dehydration step.
The mixing order of each component of the mixture is not particularly limited. In case of adding pigment and metallocene polyolefin to the aqueous solution of a dispersing agent or the aqueous dispersion of a dispersing agent, pigment and resin may be added at the same time, or pigment may be added first, followed by mixing the mixture obtained thereby and resin.
A general kneading machine or extruder may be used to manufacture the coloring resin composition. The design and operating conditions of each machine are not particularly limited.
In a preferable embodiment the composition can be manufactured as follows; the aqueous dispersion of a dispersing agent, pigment and metallocene polyolefin are mixed by a Henschel mixer or the like, and is then heated and mixed by a flusher, kneader, extruder, roll mill, ball mill, steel mill, sand mill, Attoritor, high-speed mixer, homomixer or the like; subsequently, the remaining water is removed and the mixture is pushed out under normal pressure or reduced pressure, thus manufacturing the coloring resin composition. Herein, the heating and mixing should be performed at the temperatures in which thermoplastic resin and a dispersing agent become melted. In order to further improve pigment dispersibility, the heating and mixing are preferably performed at the temperatures around the boiling point of water. In other words, processing temperature (not the setting temperature but actual heating temperature) ranges preferably from about 90xc2x0 C. to about 130xc2x0 C. Moreover, in order to efficiently dehydrate, it is preferable that a vacuum pump is connected to an extruder so as to heat, decompress and dehydrate the mixture, as required.
A colored resin molded article according to the present invention is molded from the coloring resin composition of the present invention by an optional method. The molding method is preferably extrusion molding or injection molding. The resin to be colored that is mixed with a master batch during molding is preferably the one that is compatible with thermoplastic resin used for the coloring resin composition, and may be optionally chosen. Preferable examples thereof include polyolefin resins. In order to improve physical properties, the coloring resin composition of the present invention may be mixed with resin to be colored containing a reinforcing agent such as an inorganic filler and glass fiber.
When the coloring resin composition of the present invention is extrusion-molded into particularly thin articles such as films, the films with superb pigment dispersibility and excellent surface conditions, with no cords or the like, can be efficiently provided. Moreover, when the coloring resin composition of the present invention is injection-molded, molded articles with no unevenness of color and flow marks can be provided.